Broad band antenna



y 1954 c. SHUMAKER 2,683,808

BROAD BAND ANTENNA Filed Feb. 17, 1947 OF COAXIAL LINE OFCOAXIAL LINEFREQUENCY INVENTOR. CLIFTON SHUMAKER ATTORNEY Patented July 13, 1954UNETED STATES PATENT QFFICE (Granted under Title 35, U. S. Code (1952),

sec. 266) 4 Claims.

This invention relates in general to antennas and more particularly toan antenna providing wide band frequency response characteristic.

It is an object of this invention to provide a means for extending thefrequency response band of a conventional antenna system, such as a halfWave antenna.

It is a further object of this invention to provide an antenna systemwhose frequency response characteristic is maintained substantially constant over a wide band of frequencies.

Other objects and advantages of the invention will be apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawing in which there is illustrated a preferredembodiment of the invention, and in which:

Fig. 1 shows an embodiment of the contemplated antenna arrangement andFig. 2 shows diagrammatically how the ire quency response band iswidened by the arrange ment shown in Fig. 1.

In accordance with the present invention, a wide frequency response bandis contemplated for an antenna by causing, in a sense, the antenna to beresonant at two different frequencies. This result is accomplished bycausing part of the antenna to present a very great impedance to signalshaving a certain frequency. Separate frequency response patterns may beconsidered to result from the antenna having, in effect, two differentlengths. If, now, the dimensions for the antenna are properly chosen,these patterns may be so combined that a composite frequency patternwill result which will be substantially constant in amplitude for allthe frequencies intermediate the two resonant frequencies.

In Fig. 1, to which reference is now had, one exemplary embodiment ofthe antenna arrangement is shown. This includes a half-wave antennacomprising two quarter-wave conductors ill and ii. Attached to one endof each of the conductors it and ii respectively is a cylindricalcup-like member l2 and i3. The quarter-wave conductors as and H areexcited, by means not shown, from the ends is and 15, these ends facingeach other, and the free ends of these conductors are physicallyattached to the cylindrical cups l2 and it such that they extend back toenvelope partially the conductors it and H, re-

spectively. The cu-ps i2 and 3 are so shaped that they are the samedistance from the perimeters of the conductors Iii and H along the wholelength of the cups. Since, additionally, cylinders 12 and 13 are madeconcentric with the conductors IE and II, respectively, and since theyare closed at their free ends, a shorted concentric line is formed, forthe length of the cylindrical cups [2 and It. If now the resonantfrequency of this shorted concentric line be made sufficiently differentfrom the resonant frequency of the conductors Ill and H the impedance ofthe shorted concentric line will be low as compared to the impedance ofthe conductors it and ii themselves and the response of the conductorsit and II will not be disturbed. Instead, the frequency response band ofthe conductors It and M will be slightly widened around their resonantfrequency because the cylindrical cups l2 and i3 serve to increase theeffective diameter of the conductors l6 and H with respect to th irlength. As shown in Fig. 1, the conductors it and ii are generallytubular in shape with an irregular diameter. That is, the diameter ofeach member i6 and H increases to a maximum at its mid-portion andtapers away to smaller diameters at its end, so as to increase the ratioof diameter to length. This proportion of the members it and H acts towiden further the frequency response band of the conductors I8 and Habout their resonant frequency. As thus constructed, response patternsof conductors it and H will be similar since the two conductors aredimensionally equal and each will act like a quarterwave antenna at theresonant frequency. The response patterns of the conductors iii and. i Iare shown in curve is of Fig. 2.

Curve I9 of Fig. 2 shows the response pattern which results from thereaction of the shorted concentric line formed by the conductors i2 andI3 surrounding the conductors it and l l, respectively. At theirresonant frequency, these lines will present a very great impedance toany signals and thus in effect a new half-Wave antenna will be formedwhose length is shorter than the conductors It and H by the length ofthe concentric lines. Thus a new resonant frequency will re sult fromthis shorter antenna, as shown in the curve 19. If now the curves l8 andis are combined, a curve '28 will result which will give a frequencyresponse band that is wider than the response bands of the curves :8 andis and this response band will be the frequency response pattern of theantenna arrangement shown in Fig. 1. The dimensions of the conductors i9and ii, and of the cylinders 12 and 13, may be so chosen that asubstantially constant response will be obtained for all frequenciesintermediate to the resonant frequencies of the curves l8 and it.

It should be noted that although the shorted concentric lines formedalong the length of the cylindrical cups [2 and I3 presents a very greatimpedance at the resonant frequency of the line, it tends to becomeinductive at frequencies below the resonant frequency and capacitive atfrequencies above the resonant frequency. Thus, at frequencies below theresonant frequency, the effective length of the line is increased withrespect to the diameter and at frequencies above the resonant frequency,the ratio of diameter to length is increased.

It should be further noted that the half-wave antenna arrangement shownin Fig. 1 is composed of two similar quarter-wave components. Thus, ifone of these quarter-wave components is. eliminated and the remainingcomponent is placed close to a ground plane, an image antenna willresult from the reflection produced on the ground plane by thequarter-wave antenna. Thus the quarter-wave arrangement located close toa ground plane will act like the half-wave arrangement shown in Fig. 1.

While certain preferred embodiments of this invention have beendescribed, it is realized that many modifications and variations of thisinvention may be made and no. limitations upon this invention areintended other than may beimposed by the scope of the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposewithout the payment of any royalty thereon or therefor.

What is claimed is:

1. An antenna system comprising: at least one radiating element resonantat a given frequency; and a sleeve of conducting material concentricallydisposed about the end of said radiating element and shorted thereto atthe end of said radiating element to form a section of line resonant ata second higher frequency, said sleeve being operative to effectivelyshorten the electrical 4 length of said radiating element in response tosaid second higher frequency.

2. An antenna system comprising: a pair of radiating elements resonantat a given frequency and arranged in the form of a center fed dipole,each of said radiating elements being generally tubular in shape with anirregular diameter which increases gradually from each end thereof to amaximum at its mid portion; and a cup-shaped member resonant at a secondhigher frequency, fitted over the free end of each of said radiatingelements, said last named members extending for a predetermined lengthback along the respective radiating elements toward the feed endsthereof.

3. A wide band antenna comprising: a dipole antenna resonant at a givenfrequency; and an electrically conducting member resonant at a secondhigher frequency, physically attached to the dipole only at the endthereof opposite the end to which excitation is applied and surroundingthe dipole along part of its length.

4. A Wide band antenna comprising: a center fed half wave antennaresonant at a given frequency; and an electrically-conducting memberresonant at a second higher frequency physically attached to the freeend of each half of said antenna opposite the end to which excitation isapplied and surrounding each half of the antenna along part of itslength such that the member is concentric with the half wave antenna.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,287,220 Alford June 23, 1942 2,321,454 Brown June 8, 19432,480,172 Willoughby Aug. 30, 1949 2,487,567 Lindenblad Nov. 8, 1949FOREIGN PATENTS Number Country Date 446,441 Great Britain Apr. 30 1936'

